Road construction



Nov. 1, 1932. D. MCK. HEPBURN ROAD CONS TRUCTION Filed April 25, 1927 Patented Nov. 1, 1932 UNITED STATES PATENT OFFICE DONALD MCK. HEPB'URN, PHILADELPHIA, PENNSYLVANIA, ASSIGNOR TO AMIESITE ASPHALT COMPANY OF AMERICA, 01? PHILADELPHIA, PENNS YLVANIA, A CORPO- RATION OF NEW JERSEY ROAD CONSTRUCTION Application am April 25,

The object of my invention is to provide a novel pavement or foundation of the mac-adam type offering materially greater resistance to wear by traffic than the water-bound macadam, and whose cost does not materially, if at all, exceed that of the water-bound road.

A further object of the invention is to provide a novel method for laying a macadamasphalt avement.

Maca am highways now being built are, for the most part, defective by reason of the use of water in the binder, since the fine materials which are relied upon to bind the road are soon disintegrated by the enormous suc-' tion of the tires of automobiles. In an effort to remedy this defect, so-called penetration methods have been resorted to, but these methods are expensive, and the results out of all proportion to the cost.

I have discovered ineans wherebythe .macadam type of roadway may be built with practically the same facility and at a cost no greater than the water-bound macadam, and having wearing characteristics which far surpass those of the water-bound macadam,

In the attached drawing, in which I have illustrated the various stages of a roadway built in accordance with my invention:

Figure 1 is across section of the roadbed illustrating the foundation layers of sand and broken stone; 4

Fig. 2 is a cross sectional view of the roadway showing the top dressing in place above the stone prior to the compacting operation;

Fig. 3 is a cross sectional view illustrating the finished roadway, and

Fig. 4 is a sectional view illustrating a road made in accordance with the present invention but without the sand foundation.

In making a roadway according to my invention, and with reference to the drawing, I may first lay upon the road or street a layer, 1, of sand, and upon this sand layer a loose course, 2, of clean crushed stone preferably two inches or more in thickness. I may em-" ploy stones anywhere from three-fourths of an inch to one and one-half inches in size, and even larger, but in any event the stones should be of less size than the thicknessof the finished roadbed. The depth of the sand layer 1927. Serial No. 186,304.

will be determined mainly by the size and number of the voids in the rock course and after described, I have found it preferable'to treat the crushed stone after laying, preferably by spraying, with kerosene, naphtha, gasoline or other light and more or less volatile oil. Naphtha has been found particularly desirable for the purpose. This substance functions to lay any dust, to further clean the stone, and to prepare the upper stone surfaces for the reception of the next layer orcourse to be next placed thereon.

Without rolling these bottom courses of sand and stone, I cover the stone course with a layer of an asphaltic or other bituminous mixture, 3, compounded as follows: I take all the stone passing through a threeto fiveeighths inch screen and caught on a one thirty-second inch screen, and coat the graded aggregate thus formed with kerosene. In stead of kerosene, I may employ a mixture of kerosene and a volatile solvent for bitumen such as gasoline and naphtha, and a mixture containing 50% of kerosene and 50% of gasoline or naphtha has been found satisfac-,

tory. Any of the other well known solvents or liquefiers for asphalt and other bitumens employed as a flux for these materials in road building may be used, but it is desirable to utilize, at least in part, a relatively slowly volatile material such as kerosene. Where asphalt or bitumen of high penetration is used, the aforesaid mixture of gasoline and kerosene is preferred, but where a'bitumen of low penetration is employed, I prefer to introduce with the solvents at saponifiable oil such for example as corn oil. The amount of kerosene or other liquefier employed will vary with the dryness of the stone, but I have found that for general purposes a volume of kerosene equal to 10 to 15% by Weight of the asphalt or bitumen employed in the mix gives satisfactory results. To the coated aggregate I next add hydrated or air slaked'lime or calcium oxide in quantity approximately 970 by weight of the stone content. The hydrated lime or other calcium rated in the mix, I now add a quantity of derivative having been thoroughly incorpo- 3 the asphalt or bitumen may be heated to say 200 F. to give it a workable consistency, but the other constituents of the m1x are introduced at normal temperatures, and the prodnot is preferably laid cold, it being found that the bitumen-coated mixture will not cohere and form a solid mass until spread on the roadway and compacted, provided the product is not allowed to stand sufficiently long to allow a substantial portion of the liquefier to evaporate.

As previously stated, this asphaltic or bitumen mixture is distributed over the top of the course of stone, preferably to a thickness of one inch, as indicated in the drawlng by the reference numeral 3, and the entire mass is then rolled with a heavy roller so as to compact simultaneously the bottom course of stone and the upper asphaltic course, the latter in this compacting operation being forced down into the voids between the rocks, as illustrated in Fig. 3, and the stone at the same time being forced down to a uniform penetration into the sand.

As a final step in the operation, I may then sweep he entire surface with a fine sharp sand, fil ing any voids that may remain in the surface, and the road may then be opened to trafiic.

In cases where it is desired to build up a four to six inch ma-cadam base, the above process may be repeated to obtain the desired thickness.

Preferably only sufiicient of the bitumen mix is employed to fill the voids left unfilled by the sand and to give a slight surface over the stones, which latter constitute the actual load-supportin body. As previously stated, an amount of bitumen equal to 6 to 8% by weight of the stone has been found suflicient for the purpose, but this amount may vary to some extent with size and nature of the stone used.

It will be understood that although the use of sand in the bottom course is preferred, such use is not essential. llhus I may lay the stone on the road in thinner layers so that the mass may be penetrated from the top surface with the filler described above. I may, for example, layan inch of stone on the road, covering this before rollmg with sufficient filler to fill the voids, and roll1ng the entire mass at one time. Where a greater thickness is desired, this operation may be repeated as many times as necessary to give the required thickness. Also, where sand is not available, loose earth might be used in its place.

I have found that a permanent foundation can be obtained on a road lacking sufficient capacity to carry the impact of traflic by adding four or six inches of base to the road by the above method, and if desired, an extra thickness of the binder may be added to the finished surface and rolled with a heavy roller to produce a wearing surface that will protect the heavy stone in the road from wear.

The bitumen compound hereindescribed has special advantages in the construction of roads of this type. The fact that it can be laid cold makes it possible to ship the material from a distance to, the point where the road is building and to lay it with the same, or greater, facility as the ordinary macadam. The compound further has the property of retaining its plastic condition so that it is self-healing and will not crystallize. and harden like the usual asphalt surface. 'It is further to be noted that this bituminous mixture is not laid above the stone base in a layer of any appreciable thickness and is used not as a supporting body but as a binder and filler for the stone which in reality carries the load. The small stone in the bitumen mix with the bitumen itself fills the voids in the stone .base and with the latter forms a solid mass which resists for exceptionally long periods of time the severest traffic.

In forming the bitumen compound, the lime is preferably added to the stone aggregate in advance of the bitumen whereby an especially advantageous eifect is obtained, particularly when the corn or other saponifiable oil is added with the liquefier, since this brings the lime into direct contact with the oil which advances the saponification.

The invention finds a particularly valuable application to surfacings or re-surfacings of comparative thinness and gives exceptional servlce for the materials expended and the expense of laying.

It will be understood that I do not limit the invention to the particular quantities nor to the exact character of the materials hereinbefore set forth, since'considerable modification is possible without de arture from the underlying features of t e invention. It should further be understood that the invention is not limited to the particular process of forming the bitumen mixture.

I claim:

1. The method of making roads and hig ways, which consists in laying a course of clean crushed stone of relatively large sizes free from fines, spraying said stone with a bitumen solvent, distributing thereover a bitumen-coated graded aggregate of relatively small sizes, said aggregate carrying a sufficient quantity of a slowly volatile solvent to retard the cohesion of the individual bitumen-coated particles into a solid mass at normal temperatures and being laid in an unheated condition, and rolling the said bitumen-coated aggregate into the upper voids of the lower course.

2. The method of making roads and highways, which consists in placing on the roadway, a course of sand, placing on said course of sand, an even course of loose clean stones of relatively large size, spraying said course of stone "with a liquefier, placlng, on said course of stone, a course of cold bituminous paving material comprising a graded stone aggregate of relatively small size coated with bitumen, said coated aggregate carrying a slowly volatile solvent of bitumen to retard the coherence of the bitumen coated pieces of aggregate into a solid mass at atmospheric temperatures prior to compaction on the roadway, and then subjecting the three said courses to heavy compression, effective to simultaneously force substantially all of said course of coated aggregate into the voids I at the surface of the said course of stone to bind in place the upper stones of said course of stone and to seal the surface thereof against penetration of water falling on the finished pavement, to embed the stones of said stone course into the course of sand thereunder, and to fill with sand the voids at the under surface of said course of stone.

DONALD MoK. HEPBURN. 

